Nope. Xbox is a different platform entirely so will require a new purchase and none of your routes will be carried across.
The same as all other games I would think. Buy on one platform you don't get to play them on others for free do you?
There probably are some games which have the ability to pay on one platform and use on another. I imagine Fortnite, Roblox and minecraft (ironically some of the biggest games on the planet) have this facility. You log into your account, like you would with say eBay or Amazon, it doesn’t matter what the device is. The problem with paid for games, and to a lesser degree paid content. Is that the ‘store front’ Apple, Sony, Epic, Steam and Microsoft. All take a cut. Imagine playing on PS5 and noticing that the Microsoft store has a sale so you buy on there giving them the cut, but playing it on Sony’s machine. Epic and Apple are having this argument in court. Microsoft won’t let me buy content on their Apple app. I imagine eventually it will all be available anywhere, which will be nice for us consumers.